Because a Post Type is stored in the database under the wp_posts table column post_type. The reason a post type can’t have a parent post_type is because there is no database taxonomy mapping like there is for a post categories.
Because a Post Type is stored in the database under the wp_posts table column post_type. The reason a post type can’t have a parent post_type is because there is no database taxonomy mapping like there is for a post categories.